The present invention is directed to a processing apparatus of the type which includes an upper tank and a lower tank for holding processing fluid and a narrow processing chamber located between the tanks through which a sheet of photosensitive material is advanced for processing of latent images on the material. Processing fluid is delivered to opposite sides of the photosensitive material from each of the tanks for forming a fluid layer on each side of the photosensitive material. A return drain is provided on each side of the photosensitive material for removing and returning the processing fluid to the sump tank. Examples of such devices are illustrated in U.S. Pat. Nos. 4,989,028; 4,994,840and 5,059,997. Such devices are often referred to as fluid suspension processors.
In fluid suspension processors of the prior art it is important to maintain the photosensitive material suspended in the processing fluid. It has been found that excessive contact of the photosensitive material with the sides of the processing chamber results in numerous undesirable artifacts being produced on the photosensitive material. In this regard, the prior art teaches the providing the processing fluid to the entrance of the chamber at a substantially equal pressure on both sides of the photosensitive material. In order to control the amount of fluid being removed from each side of the film, return passages, which form the drains, are adjusted in size in an attempt to control the back pressure being experienced on both sides of the film. A problem with this method is that the size of the openings is directly dependent upon the flow rate into the chamber from both the upper and lower tanks. As the flow rate fluctuates the back pressure at the drain will vary significantly such that the photosensitive material will no longer be in a stable position between the two fluid layers. This unstable condition results in the film contacting the sides of narrow processing chamber which in turn results in artifacts being formed on the photosensitive material. Controlling the flow rate is extremely difficult to accomplish and maintain in processors of the prior art. Thus, it is extremely difficult to provide a pressure balanced system in prior art processors.
The present invention is directed to solving the problems experienced in prior art fluid suspension processors by providing means for equalizing the back pressure of the processing fluid at the drains on both sides of the film so as to stabilize the photosensitive material in the chamber and thereby minimize contact with the sides of the chamber.